(1) Field of the Invention
The present invention relates to a semiconductor switch for use with a mobile communication device, and particularly to a high-frequency semiconductor switch that is used for switching between signal transmission and reception in an antenna of a mobile phone or the like.
(2) Description of the Related Art
With the recent developments in the field of mobile communications, a small, low-power high-frequency semiconductor switch has been desired as a semiconductor switch dedicated to switching between signal transmission and reception in an antenna of a mobile phone or the like. In these days, a semiconductor switch that utilizes a gallium arsenide field-effect transistor that is superior in terms of power consumption is used instead of the mainstream semiconductor switch that utilizes a silicon PIN diode.
The following describes a high-frequency semiconductor switch that utilizes such a field-effect transistor (FET). FIG. 1 is a circuit diagram showing a conventional semiconductor switch.
This semiconductor switch is made up of an input terminal 501, an output terminal 502, a through FET 505 that allows or interrupts the transmission of a high-frequency signal between the input terminal 501 and the output terminal 502, and a shunt FET 506 that connects and disconnects the output terminal 502 and the ground. In this case, the gate electrode of the through FET 505 is connected to a control terminal 503 via a resistance 507, and the gate electrode of the shunt FET 506 is connected to a control terminal 504 via a resistance 508. These resistances 507 and 508 are inserted for the protection of the gate electrodes. In general, resistances whose resistance values are several times as great as those of the characteristic impedance of a line are selected as the resistances 507 and 508.
In the semiconductor switch with the above structure, the input terminal 501 and the output terminal 502 become connected when the through FET 505 is turned to the ON-state and the shunt FET 506 is turned to the OFF-state by applying, to the control terminal 503, a voltage higher than the pinch-off voltage of the through FET 505 and by applying, to the control terminal 504, a voltage lower than the pinch-off voltage of the shunt FET 506, respectively. Meanwhile, when the through FET 505 is turned to the OFF-state and the shunt FET 506 is turned to the ON-state, the connection of the input terminal 501 and the output terminal 502 are broken, and the output terminal 502 becomes connected to the ground.
Technologies for improving the linearity in the transmission property of such a semiconductor switch described above include, for example, a method that uses FETs with different pinch-off voltages as a through FET and a shunt FET. Japanese Laid-Open Patent application No. 07-106937 discloses a semiconductor switch using this method. This technology reduces a distortion in a semiconductor switch by controlling power leakage that occurs when the shunt FET is in the OFF-state by using, for example, a FET with a pinch-off voltage of −1.0V as the through FET and a FET with a pinch-off voltage lower than 0.5V as the shunt FET. However, such a semiconductor switch has a problem of poor controllability of pinch-off voltage and an increase in the manufacturing costs since FETs with different pinch-off voltages are formed in the same substrate.